Gamma Ursae Minoris
Template:Location mark Location of γ Ursae Minoris (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Minor |
| Right ascension | Template:RA[1] |
| Declination | Template:DEC[1] |
| Apparent magnitude (V) | +3.05[2] |
| Characteristics | |
| Spectral type | A2 III[3] |
| U−B Template:Engvar | +0.08[2] |
| B−V Template:Engvar | +0.09[2] |
| Variable type | δ Sct[4] |
| Astrometry | |
| Radial velocity (Rv) | −3.9[5] km/s |
| Proper motion (μ) | RA: −17.73[1] mas/yr Dec.: +17.90[1] mas/yr |
| Parallax (π) | 6.70±0.11 mas[1] |
| Distance | Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc) |
| Absolute magnitude (MV) | –2.84[6] |
| Details | |
| Radius | 15[7] Template:Solar radius |
| Luminosity | 1,100[7] Template:Solar luminosity |
| Surface gravity (log g) | 2.53[8] cgs |
| Temperature | 8,280[9] K |
| Rotational velocity (v sin i) | 180[10] km/s |
| Metallicity [Fe/H] | {{{metal_fe2}}} dex |
| Other designations | |
| Pherkad, Pherkad Major, Gamma Ursae Minoris, 13 Ursae Minoris, HR 5735, BD+72°679, HD 137422, SAO 8220, HIP 75097 | |
| Database references | |
| SIMBAD | data |
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Gamma Ursae Minoris (γ Ursae Minoris, abbreviated Gamma UMi, γ UMi), also named Pherkad Template:IPAc-en,[11][12] is a star in the northern constellation of Ursa Minor. Together with Beta Ursae Minoris (Kochab), it forms the end of the dipper pan of the "Little Dipper", which is an asterism forming the tail of the bear. Based upon parallax measurements obtained during the Hipparcos mission, it is approximately Template:Convert from the Sun.[1]
Nomenclature
γ Ursae Minoris (Latinised to Gamma Ursae Minoris) is the star's Bayer designation. The fainter 11 Ursae Minoris has been called γ1 Ursae Minoris, in which case Gamma Ursae Minoris would be designated γ2. However this usage is rarely seen.[13]
Gamma Ursae Minoris bore the traditional name Pherkad, which derived from the Arabic فرقد farqad "calf", short for aḫfa al farkadayn "the dim one of the two calves", that is Pherkad and Kochab (the full name Ahfa al Farkadain is traditionally applied to Zeta Ursae Minoris).Script error: No such module "Unsubst". Gamma Ursae Minoris was mostly called Pherkad Major to distinguish it from Pherkad Minor (11 Ursae Minoris). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Pherkad for Gamma Ursae Minoris on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[12]
In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning North Pole, refers to an asterism consisting of Gamma Ursae Minoris, Beta Ursae Minoris, 5 Ursae Minoris, 4 Ursae Minoris and Σ 1694.[15] Consequently, the Chinese name for Gamma Ursae Minoris itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx), representing Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Crown Prince.[16]
Properties
Gamma Ursae Minoris has apparent magnitude +3.05[2] and can be readily observed with the naked eye even in a city-lit night sky. It has an absolute magnitude of –2.84.[6] Measurement of the star's spectrum resulted in a stellar classification of A2 III,[3] with the luminosity class of 'III' indicating this is an expanding giant star that left the main sequence after exhausting its core supply of hydrogen. Based on stellar evolutionary theory, Pherkad might become a Cepheid variable before settling as a red giant similar to its neighbor Kochab, before becoming a white dwarf of roughly 0.85 solar masses.[7] The effective temperature of the star's outer envelope is 8,280 K,[9] giving it the typical white hue of an A-type star.[17] It is rotating rapidly, with the projected rotational velocity of 180 km s−1[10] providing a lower limit on the azimuthal velocity along the star's equator.
This is classified as a shell star that has a circumstellar disk of gas around the star's equator, which may be causing it to vary in magnitude.[8] It is 1100 times more luminous than the Sun, and possesses a radius 15 times that of the Sun.[7]
Pherkad in fiction
Pherkad (spelled as Pherkard) features in Cthulhu Mythos.
References
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Template:Sky Template:Stars of Ursa Minor
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- ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
- ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
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